[VoiceOps] Dynamic T1 Faxing over IP

Schwarz, Albrecht (Albrecht) albrecht.schwarz at alcatel-lucent.com
Thu Dec 16 00:46:38 EST 2010

This discussion is just at the surface.
If you talk about fax over IP, then you should include the T.38 version, and there are 6 versions so far (T.38 v0 to v5).
The majority of deployed ATA's seems to use T.38 v0 from year 1998, which is an issue.
The latest one is T.38 v5 (09/2010).

If you talk about G.711 pass-through, then you should again discriminate between
a) V.152 VBDoIP with G.711 as VBD codec and
b) pseudo-VBDoIP using G.711.

The first one has a clear indication as VBD codec in the signalling plane (like SIP, H.248, H.323, etc), which allows to distinguish G.711 as audio codec and G.711 in VBD mode.
The second one is just a mess ("G.711 pass-through") due to the merge of audio with VBD (... and different media configurations).

All the requirements for FoIP and VBDoIP are e.g. summarized by ETSI TR 183 072 V3.1.1 (2010-09), Emulation Services for PSTN Modem Calls.
Which talks also about the interop issue.
And one root cause are just different T.38 implementations ...

Thus, any constructive discussion should address also that level of detail.


From: voiceops-bounces at voiceops.org [mailto:voiceops-bounces at voiceops.org] On Behalf Of Richey
Sent: Donnerstag, 16. Dezember 2010 04:53
To: voiceops at voiceops.org
Subject: Re: [VoiceOps] Dynamic T1 Faxing over IP

The TA900s and 2431s will handle faxing, alarms, modems, etc fine IF you do two things.  One you use point to point circuits between you and the IAD.  The other thing is avoid sending these accounts across sip trunks that traverse the internet.   We use a combination of PRIs for local and SIP trunks for LD.  We route the "data lines" so that their local and ld go out their closest PRI.    If the customer wants to bring their own bandwidth or they are offnet we won't support any kind of data calls.


From: voiceops-bounces at voiceops.org [mailto:voiceops-bounces at voiceops.org] On Behalf Of Jeff Anderson
Sent: Wednesday, December 15, 2010 5:54 PM
To: voiceops at voiceops.org
Subject: [VoiceOps] Dynamic T1 Faxing over IP

We are experiencing a fair amount of heart burn attempting to support faxing over our Dynamic T1 product. Some customers it works great and others have frequent problems.

We currently support dynamic T1's using both Adtran TA900 series and Cisco IAD2400 services routers. The customers fax machines will connect to their PBX that has a PRI to an IAD/TA. We have the IAD/TA configured for SIP signaling to an Acme SBC selecting T.38 as the preferred codec with fallback to g.711 pass-through. We can force a slower speed, disable error correction, disabled VAD but in the end still have very inconsistent results. From a network perspective the QoS is matching and queuing correctly, the circuits are clean and the IP SLA gives us no reason to believe they are having any network drops or jitter.

I was wondering if others who have experience with faxing over IP could share what they have learned works best or anything else that may be helpful.

Any help is greatly appreciated.


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